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    <script>
        var x = 1;
        var y = 2;
        x += y;
        // 等同于：x = x + y;
        console.log(x);

        var a = 1;
        var b = "1";
        // == 值相等
        console.log(a == b);
        // === 值相等，而且数据类型相同
        console.log(a === b);
    </script>
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